Clarify what happens when stopping and restarting PrEP in the same period

[ageorgou]

Currently this is possible, for instance:

hiv-modelling/hiv_synthesis.sas

Lines 4169 to 4177 in 689bf42

	if stop_prep_choice=1 then do;
	r=uniform(0);
	if r < eff_prob_prep_restart_choice then do; prep=1; continuous_prep_use=0.25; dt_prep_e=caldate{t}; dt_prep_rs=caldate{t}; stop_prep_choice=0; end;
	end;
	else if stop_prep_choice ne 1 then do;
	r=uniform(0);
	if r < prob_prep_restart then do; prep=1; dt_prep_e=caldate{t}; continuous_prep_use=0.25; dt_prep_c=caldate{t}; end; * dt_prep_c is prep continuation in the sense
	that they are now continuing prep again now they have np >= 1;
	end;

Should td_prep_e be the previous period?

[ageorgou]

The current structure makes it tricky. One way would be to have a variable for the date of (last) stopping and check that. Not completely clear whether dt_prep_e is always used consistently or what for!